Valve lifter with integral hydraulic lash adjuster and a method of measuring its dry length

ABSTRACT

A roller hydraulic valve lifter comprising a prior art lifter body assembly having a roller assembly at a first end for following a camshaft cam, an oil chamber connectable to an engine oil gallery, and a pushrod seat slidably disposed in an open second end and having a socket for engaging the end of a valve pushrod. A prior art hydraulic lash adjuster is disposed within the chamber. An adapter between the head of the lash adjuster and the pushrod seat transfers motion of the lash adjuster to the pushrod seat. An advantage of combining a lash adjuster with a lifter body assembly is that the lash adjuster has a passage in the head and the valve is inverted from the orientation of the original check valve. By inserting a pin through the pushrod socket, oil can be drained to permit measurement of dry length without requiring complete disassembly.

TECHNICAL FIELD

The present invention relates to hydraulic valve lifters for cams of push-rod internal combustion engines; and, more particularly, to a hydraulic valve lifter having an integral rocker arm hydraulic lash adjuster assembly replacing a prior art hydraulic plunger assembly having a solid plunger.

BACKGROUND OF THE INVENTION

Internal combustion engines having hydraulic valve lifters are well known in the automotive arts. Hydraulic lifters, also known in the art as hydraulic tappets, are currently available in mass production and incorporate integral hydraulic components to provide a simple, inexpensive package for primarily automotive and truck engines. Ease of assembly and service provide significant benefits to a cam-in-block (CIB) engine, also known in the art as a “pushrod” engine, relative to more expensive and complex multiple valve overhead cam (OHC) engines.

Various non-automotive engine manufacturers, for example, some aircraft engine manufacturers, utilize CIB engines, which have evolved relatively little in many years. In some applications, conventional hydraulic lifter assemblies cannot be used as received from a lifter manufacturer because a typical hydraulic lifter lacks the total adjustment range necessary for a “net build” engine assembly, employing identical standard-length pushrods. Therefore, in manufacturing these engines with hydraulic lifters, some engine manufacturers require the capability in a lifter to disassemble the lifter and measure the solid height of each individual component. The heights are summed to establish a predetermined dry valve stem clearance; then a pushrod of predetermined length is selected for each cylinder from an array of pushrod lengths so that the lifter can operate within its desired operating range.

A serious problem exists in using prior art lifters in this manufacturing scheme because commercially-available lifters are self-contained, that is, the body and plunger are matched to achieve a nominal leakdown rate and are not well-suited for disassembly and reassembly after measurement. Disassembly requires removal of internal fluids supplied within the lifters by the manufacturer, but the fluids are trapped in a reservoir which is inaccessible except by disassembly of the lifter. Further, reassembly is vulnerable to potential quality issues associated with lifter mis-builds, including damaging of valve train dynamics and objectionable valve clatter resulting from lack of oil in the high-pressure chamber of a lifter at engine start-up. For these reasons, OEM manufacturers of hydraulic lifters do not recommend such disassembly and reassembly.

What is needed is means for providing a hydraulic lifter that may be readily drained and refilled to permit simple measurement of the “dry” height of a lifter without disassembly.

What is further needed is a simple, inexpensive, and drainable hydraulic lifter that may be assembled from prior art lifter and hydraulic lash adjuster components.

It is a principal object of the present invention to provide an improved hydraulic lifter that is readily drained and refilled to permit simple measurement of the “dry” height of a lifter without disassembly.

SUMMARY OF THE INVENTION

Briefly described, an improved roller hydraulic valve lifter (RHVL) comprises a prior art lifter body having a roller assembly at a first end for following a camshaft cam, a large internal oil chamber connectable to an engine oil gallery, and a pushrod seat slidably disposed in an open second end and having a socket for engaging the end of a valve pushrod. A commercially-available hydraulic lash adjuster (HLA), manufactured for use as a lash-adjusting pivot for a rocker arm in an overhead valve engine, is disposed within the internal chamber of the RHVL body in place of the originally-provided solid plunger, spring, and check valve. A socket-faced adapter, which may be an inverted prior art pushrod seat, is slidably disposed between the hemispherical head of the HLA and the RHVL pushrod seat to transfer motion of the HLA to the pushrod seat.

An important advantage of the combination of HLA within an RHVL body is that the HLA has an oil passage in the tip of the hemispherical head and the HLA check valve is inverted from the orientation of the original check valve in the RHVL. Thus, by inserting a pin through the pushrod socket and into the HLA assembly, oil can be readily drained from behind the check valve to permit easy measurement of overall dry length without requiring any disassembly and reassembly. Further, the HLA chamber is readily refilled after such measurement, and further, the HLA is completely bathed in engine oil during operation and therefore is immune to deflation and air embolism during periods of engine shutdown.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is an elevational cross-sectional view of a prior art hydraulic valve lifter, showing an internal hydraulic plunger mechanism;

FIG. 2 is an elevational cross-sectional view of a prior art roller hydraulic valve lifter body assembly without a prior art internal hydraulic plunger mechanism;

FIG. 3 is an elevational cross-sectional view of a prior art hydraulic lash adjuster as manufactured for use as a lash-adjusting pivot for a valve train rocker arm in an overhead valve engine; and

FIG. 4 is an elevational cross-sectional view of a prior art hydraulic lifter pushrod seat; and

FIG. 5 is an elevational cross-sectional view of an improved roller hydraulic valve lifter assembled from the prior art components shown in FIGS. 2 through 4, in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hydraulic valve lifters as a class are intended to adapt in length to remove lash in a valve train of an internal combustion engine, thereby optimizing the opening and closing performance of the intake and exhaust valves and minimizing the clatter of valve stems against tappets. Early hydraulic lifters were so-called mushroom or slider lifters (SHVL) wherein the surface of a foot on the lifter slidingly followed a rotating cam lobe.

Although the foot was bathed in oil during engine operation, engines thus equipped suffered from frictional wear of the cam and lifter foot, which tended to occur especially upon starting of the engine when the interface was drained of oil. More recently, in hydraulic valve lifters a precision roller replaces the slider foot for following the cam lobe (RHVL), with reduced wear to the lifter and the cam lobe. It should be understood that an improved hydraulic valve lifter in accordance with the invention may be formed as either an SHVL or an RHVL, although for convenience only the RHVL version is exemplarily shown below.

Referring to FIG. 1, a prior art SHVL 10 is shown for the purpose of illustrating the components replaced in an improved lifter in accordance with the invention. Lifter 10 comprises a generally cup-shaped cylindrical body 12 having a blind bore 14 that opens at a first end 16 and is closed at a second end 17 in the form of a slider foot 18 at a second end for following a cam lobe (not shown). A pushrod seat 20 is slidably disposed in bore 14 at open end 16 and includes a socket 22 for receiving a ball-end pushrod (not shown). Within bore 14 is slidingly disposed a plunger and valve subassembly 24. A plunger body 26 is slidably disposed within bore 14 and itself includes an inner bore 28. A solid plunger 30 having a cap 31 is urged against pushrod seat 20 by a spring 32 anchored on a shoulder in bore 28. A ball cage 34 containing a check ball 36 is fixedly disposed in an axial passage 38 in plunger body 26 adjacent a valve seat 40 having an axial feed tube 42 extending into a low-pressure oil reservoir 44 formed at the inner end of blind bore 14. A high-pressure chamber 45, containing ball cage 34 and check ball 36, is formed between valve seat 40 and plunger 30, which chamber expands by filling with oil from feed tube 42 and reservoir 44 as spring 32 urges plunger 30 and seat 20 outwards of body 12 to remove lash in the valve train. Oil is supplied into the lifter via a port 46 through wall 48 of body 26 in communication with an engine oil gallery (not shown) via an annular groove 50. As noted above, and below in FIG. 2, foot 18 may be replaced by a roller (not shown in FIG. 1).

As further noted above, a serious problem exists in adapting lifter 10 for use in an engine having close valve train tolerances. To measure the net mechanical length of lifter 10 from foot 18 to socket 22 requires that high-pressure chamber 45 be completely compressed such that plunger 30 rests against cage 34. But oil can escape from chamber 45 only via a clearance between plunger 30 and bore 28 or through valve seat 40. Check ball 36 cannot be reached mechanically to relieve oil through the valve seat, so either the lifter must be disassembled and then reassembled, or the lifter must be subjected to high axial pressure for an extended period of time to force the oil in chamber 45 past plunger 30. Neither option is attractive from an engine manufacturing point of view.

Referring to FIG. 2, a lifter body assembly 10′ includes a lifter body 12′ similar to lifter body 12 except that body 12′ is provided with a roller foot 18′ comprising a roller well 52 housing a roller 54 rotatably disposed on a shaft 56 extending across well 52. A pushrod seat 20′ is slidably disposed at the open end 16′ of blind bore 14′, forming a chamber 44′ suppliable with oil via port 46′. An axial passage 58 extends through seat 20′ from socket 22′ to chamber 44′.

Referring now to FIG. 3, a prior art hydraulic lash adjuster (HLA) 60 comprises a cup-shaped adjuster body 62 having a blind bore 64 defining an open end 66 and a closed end 68. A plunger 70 having a hemispherical outer end 72 is slidingly disposed within bore 64 and is constrained therein by a stop ring 74 and clip 76. Plunger 70 is hollow and contains a reservoir 78 communicating with an axial passage 80 through end 72 and supplied with oil via ports 73,75. A high pressure chamber 82 is defined in bore 64 between plunger 70 and end 68. A valve seat 84 is defined in plunger 70 and includes an axial passage 86 extending between reservoir 78 and chamber 82 for providing oil thereto. A check ball 88, contained in a cage 90, forms a check valve with seat 84. A lash adjustment spring 92 is disposed between a well 94 in closed end 68 and plunger 70. Well 94 receives cage 90 and thus permits plunger 70 to operate over a lash-adjustment distance 96.

Referring now to FIGS. 2 through 5, an improved roller hydraulic valve lifter 110 incorporates prior art HLA 60 into prior art lifter body assembly 10′ to form an RHVL that can be deflated simply by insertion of a pin from open end 16′ of body 12′. End 68 of HLA 60 is disposed in a recess 101 in closed end 17′ of body 12′. The outer diameter of is HLA 60 is preferably less than the inner diameter of chamber 44′, creating an annular chamber 144 surrounding HLA 60, which chamber is filled with oil from port 46′ during operation of lifter 110. Reservoir 78 is filled with oil from chamber 144 via ports 73,75.

Still referring to FIGS. 2 through 5, adapter 220 (FIG. 4) formed from a pushrod seat of a commercially-available smaller-diameter RHVL, is disposed between outer end 72 and seat 20′, includes a socket 222 having a shape accommodating the radius of HLA head 72 and a passage 258 extending through adapter 220. When inverted, adapter/seat 220 is disposed within a stepped recess 202 in seat 20′, defining a spacer between HLA head 72 and pushrod seat 20′, and further defining a space 204 therebetween. As is known in the prior art, face 21′ (FIG. 2) of seat 20′ and face 221 of seat 220 are each slightly radiused.

To measure the deflated length of lifter 110 that has been previously filled with oil in high pressure chamber 82, pin 98 is inserted through axial passage 58, through passages 258 and 80, and into valve seat passage 86. The pin is then used to move check ball 88 away from mating engagement with seat 84 thereby releasing the oil from high pressure chamber 82. Upon release of the oil, plunger 70, and seats 220 and 20′, move toward high pressure chamber 82 reducing the lifter assembly to its dry or mechanical length. In that state, the mechanical length of the lifter can be measured between any two reference points such as, for example, between a first body reference point 99 and a second plunger reference point 100.

Optionally, a flat disk 206 may be installed in space 204 which functions in known fashion as a metering valve for oil flow between passages 58 and 258. Of course, a disadvantage of incorporating disk 206 is that check ball 88 then is not directly accessible by a pin via passages 58,258,80,86 to relieve oil pressure in high-pressure chamber 82 and in order to measure directly the deflated length of lifter 110. Such measurement then requires partial disassembly of lifter 110, removing pushrod seat 20′ and disk 206, a minor inconvenience. Of course, if metering oil flow from lifter 110 is not needed, a unified pushrod seat (not shown) may be fabricated, combining sockets 22′ and 222 in a single element. However, an advantage of an RHVL in accordance with embodiment 110 as shown in FIG. 5 is that the lifter may immediately be assembled from off-the-shelf prior art components: roller lifter body 12′, pushrod seat 20′, HLA 60, and pushrod seat 220. Such assembly requires no additional machining or fabrication of parts, provided that components of correct size are selected from the array of components existing in the commercially-available art.

While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims. 

1. A hydraulic valve lifter assembly for transmitting motion of a camshaft lobe to a pushrod in an internal combustion engine, comprising: a) a hydraulic lifter body having a blind bore having an open end and a closed end; b) a pushrod seat slidably disposed in said blind bore at said open end to define a chamber in said lifter body assembly; c) a hydraulic lash adjuster disposed in said chamber and having a lash adjuster body, and a plunger slidably disposed in said lash adjuster body, said plunger having a head extending from said lash adjuster body, said plunger being hollow to define an oil reservoir therewithin, said plunger including a check valve in communication with said reservoir and disposed in a high-pressure chamber between said plunger and said lash adjuster body; and d) an adapter disposed between said plunger head and said pushrod seat.
 2. A hydraulic valve lifter assembly in accordance with claim 1 further comprising a slider disposed at said closed end of said lifter body for following a cam lobe.
 3. A hydraulic valve lifter assembly in accordance with claim 2, wherein said slider is selected from the group consisting of a slider foot and a roller.
 4. A hydraulic valve lifter assembly in accordance with claim 1 wherein said chamber is defined by a space between said hydraulic lash adjuster and said blind bore of said body.
 5. A hydraulic valve lifter assembly in accordance with claim 4 wherein said chamber is an oil reservoir communicable with an oil gallery of said engine.
 6. A hydraulic valve lifter assembly in accordance with claim 4 wherein said plunger head includes an axial passage defining a communication between said chamber and said oil reservoir within said plunger.
 7. A hydraulic valve lifter assembly in accordance with claim 1 wherein a linear axial opening exists through said pushrod seat, through said adapter means, and through said plunger to said check valve.
 8. A hydraulic valve lifter assembly in accordance with claim 1 further comprising a metering disk disposed between said pushrod seat and said adapter.
 9. A hydraulic valve lifter assembly in accordance with claim 1 wherein said pushrod seat and said adapter are formed as one piece.
 10. A method of measuring a net mechanical length of a hydraulic valve lifter assembly initially filled with oil, said assembly including a hydraulic lash adjuster disposed in a bore of a lifter body, and a pushrod seat assembly disposed proximate said lash adjuster, wherein said lash adjuster further includes a valve assembly having a seat and a valve selectively seatable against said seat, and a high pressure chamber defined by a space between said valve assembly and said body, said seat assembly, lash adjuster and seat of said valve assembly having axially aligned openings, the method of measuring a net mechanical length of a hydraulic valve lifter assembly initially filled with oil including: a) inserting a pin through said opening in said seat assembly, said opening in said lash adjuster and said opening in said seat of said valve assembly; b) moving said valve away from said valve seat to open said valve assembly; c) releasing oil from said high pressure chamber; and d) measuring the net mechanical length of the valve lifter assembly taken from a reference point on said body and a reference point on said pushrod seat assembly.
 11. A method of measuring a net mechanical length of a hydraulic valve lifter assembly in accordance with claim 10, wherein said pushrod seat assembly includes a pushrod seat, an adapter and a metering valve disposed between said seat and adapter, said method including the step of removing said metering valve from said hydraulic valve lifter assembly before inserting said pin. 